Gasification is a partial oxidation process that generates gases from the injection of carbonaceous feed, steam, and oxygen. Feed, steam, and oxygen are injected into the gasification chamber through a feed-injector. Typically, the feed-injector has a feed channel and one or two oxygen channels so that the feed remains isolated from the oxygen until exiting the feed injector at the feed-injector tip. Because gasification is an exothermic process, the temperatures within the gasification chamber typically range from approximately 2000xc2x0 F. (1093xc2x0 C.) to approximately 2700xc2x0 F. (1482xc2x0 C.).
One knowledgeable in the art should appreciate that the operation of the gasification chamber depends upon the condition and design of the feed-injector. For example if the feed-injector tip is burned or thermally deformed, the slurry and oxygen may mix prematurely which may create inefficient operation of the unit or unsafe operating conditions. In order to reduce the likelihood of damaging the feed-injector tip, a cooling system coupled to a cooling jacket or cooling coils around the tip of the feed injector is used to keep the temperature of the feed-injector tip within a given tolerance range. The presence of a leak in the cooling system, may allow carbon monoxide, synthesis gas or other gases to enter the cooling system because the gas pressure of the reactor is significantly higher than the pressure in the cooling system. As a result of even a very fine leak, significant gas may enter the cooling system and lead to improper cooling of the feed-injector tip and poor reactor performance. Further, the presence of synthesis gas in the cooling system may lead to the build-up of hydrogen and carbon monoxide gas which in turn may lead to explosion within the cooling system. For this reason it should be recognized by one of skill in the art that a detection system to detect entrapped gas caused by leaks in the cooling system is important to the safe and efficient operation of a gasification unit.
One type of conventional gas detection system that attempts to detect leaks utilizes gas sensitive probes to monitor the presence of gases, such as carbon monoxide, air, and so forth in the cooling system. In such a system, the coolant, typically water or treated cooling water, travels through a coolant supply channel and encounters the feed-injector tip and becomes hot and in turn travels through a coolant return channel. The hot coolant is routed back to a heat exchanger where the heat is removed and the coolant is returned to the coolant supply channel for further use. A leak in the system may cause gases to be entrapped into the cooling system, especially if the leak occurs at the feed injector. When gas is entrapped in the cooling system, the gas bubbles can be caused to naturally float upward into a leak detection channel which is an alternative branch of the return channel. Ideally the amount of gas is detected by a gas sensor located at a high point or at the top of the leak detection channel. In the presence of gas, the gas sensor generates an electronic signal that could be routed to a control system; the control system could activate an alarm if the amount of gas present indicates that a leak has occurred within the cooling system and corrective action may be taken.
Under ideal circumstances, such a gas detection system would detect a leak in the coolant system before the feed-injector tip becomes damaged. In reality, the above described gas detection system has difficulty detecting a leak because it is extremely difficult to remove all of the gas from the cooling system. Thus, it is not uncommon that the gas sensor becomes saturated even when there are no leaks in the cooling system. One of skill in the art should understand that the saturation of the gas sensor makes the detection of gas entrapped by leaks in the cooling system very difficult.
Alternatively one can carefully monitor the pH of the coolant for changes that may be due to the entrapment of gas and thus leaks. However, the use of such a system is limited to situations in which acidic gas, such as carbon dioxide, hydrogen sulfide, nitrogen oxides, sulfur oxides, etc. are being entrapped in the cooling system. An additional limitation is that coolant solutions, especially aqueous coolants, are often treated with basic compounds so as to minimize corrosion. One of skill in the art would readily appreciate that the entrapped acidic gases may react with the corrosion prevention treatments and thus the leak may go undetected for a considerable amount of time.
Thus, it would be beneficial to have an apparatus and method for detecting leaks in a cooling system that is capable of overcoming the shortcomings of conventional detection methods.
The present invention is generally directed to an optical gas detector for use in cooling systems, particularly cooling systems associated with a gasification unit. In one illustrative embodiment, the detection system includes a light source, a light detector, a conversion devise, and a control system. The light source should be operatively coupled to a first optical fiber the first optical fiber connecting the light source to a first probe the first probe being functionally effective to transmit light. The light detector should be coupled to a second optical fiber, the second optical fiber connecting the light detector to a second probe, the second probe being functionally effective to receive light from the light source. The conversion device should be operatively coupled to the light detector, the conversion device generating an adjusted electronic signal in response to the light emitted by the light source and received by the light detector. The control system receives the adjusted electronic signal from the conversion device with the control system functionally responding to the electronic signal to provide an indication of at least one leak in the pressurized cooling system. The detection of the leak is due to the variability of the adjusted electronic signal with traversal of a gas bubble across an optical path formed between the light source and the light detector. In one illustrative embodiment, at least one of the probes is selected from a group consisting of a high-pressure probe, a high-temperature probe and a high-pressure high-temperature probe and preferably at least one of the probes is a sapphire probe. In another embodiment the light source may be a coherent light source or it may be a collimated light source that is not coherent. The light detector may be selected from the group including a photodiode, phototransistor, photomultiplier tube, and a charged-coupled device.